This invention relates to an improved dehydrogenation process for producing indene and substituted indenes, and more particularly, to a multi-stage dehydrogenation process.
Indene is present in low concentrations (e.g. 12-16%) in ethylene or gas oil cracking coproducts, but is has been difficult to recover the indene in satisfactory yields and purity from these low concentration sources. Indene is a desirable raw material for preparing superior heat-resistant polymers.
The invention of this application is directed particularly to the preparation of indene and substituted indene from tetrahydroindene and substituted tetrahydroindene. Tetrahydroindene along with other products are formed in Diels-Alder reactions of butadiene with cyclopentadiene or its dimer, dicyclopentadiene. Substituted tetrahydroindenes are obtained when a substituted butadiene is used in the reaction. A considerable amount of research has been conducted and published on this reaction, and various suggestions have been made for optimizing the production of the various coproducts such as vinyl cyclohexene and vinyl norbornene.
The dehydrogenation of indene precursors such as tetrahydroindene into indene has been described in the art and generally is conducted in the presence of dehydrogenation promoting catalysts. In U.S. Pat. No. 4,143,082, the dehydrogenation of indene precursors into indene is accomplished by contacting the indene precursor in the presence of an oxygen donor with a phosphate catalyst at elevated temperature. These catalsyts, described more fully in the patent, are salts of one of the phosphoric acids. Other types of dehydrogenation catalyst have been described in the literature, and such compounds include the metal oxides, metal salts such as the halides, phosphates, sulfates, molybdates, tungstates, etc. Generally, these catalysts are characterized as compounds containing a metal having a polyoxidation state, that is, a metal having at least two oxidation states in addition to the zero state. Examples of useful polyoxidation state metals include Ti,V,Cr,Mn,Co,Ni,Cu,Nb,Mo,Ru, etc.
In addition to the use of polyoxidative state metals, oxidation catalysts also may be combined with one or more monooxidation state metals which act as promoters, initiators, stabilizers and the like. The single oxidation state metal or metal compounds include the alkali metals, and polyvalent metals such as magnesium, aluminum, calcium, scandium, zinc, etc. The use of cobalt and molybdenum oxides promoted with potassium oxide in dehydrogenating indane to indene is reported in Czech U.S. Pat. No. 135,251. The catalyst bed contained 3% CoO, 10% MoO.sub.3 and 0.3% K.sub.2 O. A review of the various catalysts useful in oxidative dehydrogenation of organic compounds is found in U.S. Pat. No. 3,925,498. U.S. Pat. No. 3,887,631 describes the oxidative dehydrogenation of hydrocarbons such as butene and ethylhexane by use of a catalyst consisting essentially of the oxides of molybdenum, cobalt and boron.
U.S. Pat. No. 3,925,498 describes an oxidative dehydrogenation procedure which utilizes a multiple bed reactor and wherein incremental amounts of oxygen are added to the organic compounds to be dehydrogenated as the organic compounds pass through the reactor. The mixing of the oxygen and the organic compounds occurs in those areas where the catalyst is not present.